Lubricating oil compositions

ABSTRACT

A lubricating oil composition having good antiwear and load carrying properties comprises a lubricating oil and a mixture of (a) a quaternary hydrocarbyl ammonium salt of a mono (C1 C4) alkyl dihydrogen phosphate and (b) a quaternary hydrocarbyl ammonium salt of a di-(C1 - C4) alkyl hydrogen phosphate, e.g. tetrabutyl ammonium salts of mixtures of methyl hydrogen phosphate and dimethyl hydrogen phosphate.

United States Patent Jervis et a1. 1 1 Jan. 7, 1975 [54] LUBRICATING OILCOMPOSITIONS 3,720,612 3/1973 Bosniack et al. 252/325 [75] lnventors:Graham James Jervis, Abingdon; FOREIGN PATENTS OR APPLICATIONS R r R n,g both f 7,006,203 11/1970 Netherlands 252/325 England 1,199,015 7/1970Great Britain 252/325 Assigneez E580 Research and Engineering 1,230,0354/1971 Great Britain 252/325 Company Linden Primary ExaminerPatrick P.Garvin [22] Filed: Nov. 15, 1972 Assistant ExaminerAndrew H. Metz [211pp NO: 306,850 Attorney, Agent, or F1rmByron O. D1mm1ck [57] ABSTRACTForeign Application Priority Data A lubricating oil composition havinggood antiwear Nov. 24, 1971 Great Britain 54577/71 and load carryingproperties comprises a lubricating oil and a mixture of (a) a quaternaryhydrocarbyl am- [52] US. Cl. 252/325 monium salt of a mono (C C alkyldihydrogen [51] Int. Cl ClOm 3/38 phosphate and (b) a quaternaryhydrocarbyl ammo- [58] Field of Search 252/325 nium salt of a di-(C, Calkyl hydrogen phosphate, e.g. tetrabutyl ammonium salts of mixtures ofmethyl [56] References Cited hydrogen phosphate and dimethyl hydrogenphos- UNITED STATES PATENTS P 8/1951 Werntz 252/325 X 7 Claims, NoDrawings LUBRICATING OIL COMPDSITIONS This invention relates tolubricating oil compositions containing amine salts of phosphoric acids.

Lubricating oils usually require additives to improve the anti-wear andload carrying properties of the oil, and this is especially the case foraircraft lubricating oils, e.g. aviation turbine lubricants. Certainamine salts of phosphoric and thiophosphoric acids have been proposedpreviously as anti-wear additives, but although some show good anti-wearproperties they are corrosive and/or incompatible with siliconeelastomers. We have now found certain amine salts which not only showgood anti-wear or extreme pressure properties, but also have goodsilicone elastomer compatibility. They also show good corrosionproperties.

According to this invention a lubricating oil composition comprises alubricating oil and a mixture of certain amine salts. This mixturecomprises (a) a quaternary hydroearbyl ammonium salt of a mono (C Calkyl dihydrogen phosphate of the formula and (b) a quaternaryhydrocarbyl ammonium salt of di-(C C alkyl hydrogen phosphate of theformula R O ONRABJRHU where R, R R and R are similar or dissimilarhydrocarbyl groups, R, R R and R containing a total of at least 10carbon atoms, and R and R similar or dissimilar are C C, alkyl groups.

The total number of carbon atoms in R, R R and R must be at least and ispreferably more, e.g. at least 14. This means that although one or moreof the groups can be relatively short chain, e.g. methyl, or ethyl, oneor more of the other groups must be long chain, e.g. decyl, dodecyl,etc. When the mixture of amine salts is added to mineral oils thepreferred maximum number of carbon atoms in R, R R and R is 100, whereaswhen the mixture is added to synthetic ester oils the preferred maximumnumber of carbon atoms is 40. Although the groups R, R R and R can bedifferent, in practice it is preferred that at least two of the groupsbe the same, e.g. R R methyl, R ethyl, and R octadecyl; or R R methyl,and R R octadecyl. The groups R, R, R and R may be straight-chain orbranched-chain. R, R R and R may be alkaryl, aralkyl, cycloalkyl, oraryl, but they are preferably alkyl groups. Thus, one or more of thegroups R, R, R and R may be methyl, ethyl, npropyl, iso-butyl, n-hexyl,n-decyl, Z-ethyl decyl, noctadecyl, m-tolyl, p-ethyl phenyl, benxyl,cyclooctyl, phenyl, or naphthyl; provided the total number of carbonatoms int he four groups is at least 10. Particularly preferred casesare where at least three of the groups s R, R, R and R are the samealkyl groups, e.g. all the same such as n-butyl, or three are octyl asin hexyl trioctyl ammonium salts.

Although each of the groups R, R R and R are termed hydrocarbyl groups,they may however be substituted by polar substituents, e.g. chlorine, orbromine atoms or keto or ethereal groups, provided these substituentsare not present in proportions sufficiently large to alter significantlythe hydrocarbon character of the group; e.g. the groups contain no morethan l()% by weight of polar substituent based on the weight of thehydrocarbyl portion of the group.

The groups R and R are alkyl groups containing l, 2, 3 or 4 carbonatoms, i.e. they are methyl, ethyl, npropyl, iso-propyl, n-butyl,sec-butyl, or iso-butyl groups. It is preferred that both R and R arethe same, e.g. both methyl groups or both ethyl groups. Particularlypreferred salts are mixtures of tetra-n-butyl ammonium salts of dimethyl hydrogen phosphate and methyl di hydrogen phosphate and mixturesof hexyl trioctyl ammonium salts of methyl dihydrogen phosphate anddimethyl hydrogen phosphate.

The mixture of acid phosphates from which the quaternary ammonium salts(a) and (b) are derived is best prepared by reacting phosphoruspentoxide with a C C, alcohol or mixture of alcohols, in a proportion ofabout 3 moles of alcohol per mole of pentoxide. A mixture of alkylphosphates is obtained according to the following reaction.

P20 BROII In practice the phosphorus pentoxide can be stirred vigorouslyin dry ether and the alcohol is added dropwise at a rate sufficient tocause the ether to reflux gently. The product may thereafter be filteredto remove any unreacted phosphorus pentoxide, and the ether removed byevaporation under vacuum.

The mixture of alkyl phosphates thus obtained is reacted with aquaternary ammonium hydroxide solution (e.g. 40% aqueous). Suchsolutions may be conveniently prepared by reacting at ambienttemperature a tertiary amine with an alkyl halide to form the quaternaryammonium halide.

This halide is mixed with a solution of silver oxide in water, and thereaction mixture is agitated. Silver halide is precipitated and asolution containing quaternary ammonium cations and hydroxide anions isobtained. Alternatively the quaternary ammonium halide can be convertedto the corresponding hydroxide by the use of a suitable ion exchangeresin, e.g. a polystyrene divinyl benzene copolymer substituted withtertiary amine groups.

On reacting such quaternary ammonium hydroxide solutions with themixture of alkyl phosphates, the desired mixture of amines salts (a) and(b) is formed. The mole ratio of (a) to (b) prepared by these methods isapproximately 1:1, and this is the preferred ratio.

The amount of the amine salt mixture added to a lubricating oil,especially an aviation turbine oil, is usually a minor proportion,preferably 0.001 to 10.0% by weight, e.g. 0.01 to 5.0% by weight, basedon the weight of lubricating oil.

The lubricating oil can be any mineral, animal, fish, vegetable orsynthetic oil, for example, petroleum oil fractions ranging from spindleoil to SAE 30, 40 or 50 lubricating oil grades, castor oil, animal orfish oils or oxidised mineral oil, e.g. palm oil, lard oil, tallow oil,arachis oil or sperm oil.

The preferred lubricating oil is a synthetic ester and suitable diestersinclude diesters of the general formula ROOCRCOOR and RCOOROOCR where Rrepresents a C to C alkyl group, while R represents a C to C saturatedaliphatic hydrocarbon group or an ether-interrupted saturated aliphatichydrocarbon group. The above types of esters may be prepared fromalcohols and dicarboxylic acids or glycols and monocarboxylic acids.

Another suitable class of ester lubricant are the polyesters which areprepared by reacting polyhydric alcohols eg those having 2 to 12hydroxyl groups per molecule and 2 to 40 carbon atoms per molecule, suchas trimethylolpropane, pentaerythritol and dipentaerythritol withmonoand/or di-carboxylic acids such as butyric acid, caproic acid,caprylic acid and pelargonic acid, or adipic, sebacic or azelaic acids.

The complex esters which may be used as base oils are formed byesterification reactions between a dicarboxylic acid, a glycol and analcohol and/or a monocarboxylic acid. These esters may be represented bythe following formulae:

R (OOCR COO-R ),,OOCR wherein R represents alkyl radicals derived from amonohydric alcohol, R represents hydrocarbon radicals derived from adicarboxylic acid, e.g. alkanedioic acids, R represents divalenthydrocarbon or hydrocarbonoxy radicals such as CH (CH or -CH CH- (OCH CHor CH CH(CH (OCH CH(CH derived from an alkylene glycol orpolyalkyleneglycol, while R represents the alkyl group derived from amonocarboxylic acid. n in the complex ester molecule which is an integerwill usually range from 1 to 6 depending upon the product viscositydesired which is controlled by the relative molar ratio of the glycol orpolyglycol to the dicarboxylic acid. In preparing the complex ester,there will always be some simple ester formed, i.e. n=0, but this willgenerally be a minor portion. In general these complex esters will havea total of between and 80, e.g. between and 65 carbon atoms permolecule.

Particularly suitable lubricants are esters of polyhydric alcoholshaving the formula R- -CH2OH where R is a -CH OH group or an alkylgroup, e.g. an alkyl group containing 1 to 6 carbon atoms. Thus,suitable esters of this type are the neopentyl polyol esters oftrimethylol ethane, trimethylol propane, trimethylol butane and ofpentaerythritol or di-pentaerythritol.

The preferred acids used to esterify trimethylol propane are the C to Cmonocarboxylic acids. Particularly preferred are the C C esters, e.g. C(caprylic) and C (pelargonic) acid esters. Mixtures of these C-,C acidsmay be used. When such an acid mixture is used, it is preferred that themixture average between C and C Although more difficult to form, it iseven more preferred that one methylol group be esterified with aneo-heptanoic acid, e.g. 2,2-dimethylpentanoic acid, and the remainingmethylol groups esterified with non-hindered acids, e.g. pelargonicacid. This particular ester is substantially as thermally stable as thecompletely hindered ester but has superior volatility and lowtemperature characteristics.

The preferred acids used to esterify pentaerythritol are the C.,-Cmonocarboxylic acids with the more preferred esters being those of C toC acids, e.g. nvaleric, isovaleric, 2-ethyl butyric, caproic,n-heptylic, n-octanoic or 2-ethyl hexoic acids or a mixture of C to Cacids.

Blends of diesters with minor proportions of one or more thickeningagents may also be used as lubricants. Thus one may use blendscontaining up to 50% by volume of one or more water insolublepolyoxyalkylene glycols, for example, polyethylene or polypropyleneglycol, or mixed oxyethylene/oxypropylene glycol.

Formulations suitable for gas turbine lubrication include from 65 tovol.% of one or more diesters of azelaic or sebacic acid and a C -Cbranched chain alcohol, particularly of 2-ethyl hexanol, or 0x0 alcoholsconsisting predominantly of C C or C alcohols,

or of mixtures of such alcohols, and 35 to 10% of polyoxyalkylene glycolether represented by the general formula:

wherein R R and R are hydrogen or C -C alkyl groups and wherein not morethan two such groups is hydrogen, and n is an integer greater than 1.Particularly useful compounds are poly-oxypropylene glycol andmono-ethers and the corresponding diethers.

The thermal stability of such diester/polyoxyalkylene glycol ethers maybe improved if a small proportion of a complex ester derived from threeor more carboxylic acids or alcohols, at least two of which aredifunctional acids or alcohols is incorporated. Such complex esters maybe glycolor dicarboxylic acid centered, the molecule being terminatedwith a mono-hydroxy or monocarboxylic acid compound. A particularlypreferred complex ester of this type is derived from polyethylene glycolof molecular weight 200, 2 molecules of sebacic or azelaic acid, and 2molecules of a C -C branched chain aliphatic monohydric alcohol,particularly 2- ethyl hexanol.

Other additives which may be incorporated in the lubricating oil includecorrosion inhibitors, e.g. sebacic acid, a metal deactivator such asquinizarin, a foam inhibitor, e.g. a silicone polymer such as dimethylsilicone, an antioxidant, e.g. phenothiazine or dioctyl diphenylamine;or an antiwear additive, e.g. tricresylphosphate. Alternatively themixture of amine salts can be added to a liquid fuel oil, e.g. a dieselfuel oil.

EXAMPLE 1 Tetrabutyl ammonium salts of mixtures of l methyl dihydrogenphosphate and di-methyl hydrogen phosphate (2) ethyl dihydrogenphosphate and di-ethyl hydrogen phosphate, and (3) n-butyl dihydrogenphosphate and di-n-butyl hydrogen phosphate were prepared according tothe following procedure.

A aqueous solution of the acid phosphate was stirred and tetra-n-butylammonium hydroxide solution (40% aq.) was added to adjust the pH to 7.The solution was evaporated to dryness in the presence of a trace ofn-octanol to inhibit foaming. Toluene was added and the solution againevaporated to dryness: this was repeated once to ensure an anhydrousproduct.

For comparison purposes tetrabutyl ammonium salts of mixtures of C C andC n-alkyl dihydrogen and di-n-a1kyl hydrogen phosphates were alsoprepared.

Each mixture was separately added to a synthetic ester base oil whichalso contained 1.0% by weight of tricresyl phosphate, 1.6% by weight ofdioctyl diphenyl amine, and 0.4% by weight of phenothiazine. The baseoil was a mixture of esters obtained by the esterification of 90% byweight pentaerythritol and 10% by weight dipentaerythritol with amixture of (C -C fatty acids.

The IAE gear machine failure load at 110C/2000 RPM and the Rolls RoyceSilicone Elastomer zero swell temperature (C) were determined. Thestandard Rolls Royce silicone elastomer compatibility test (Method1,009) involves the immersion of a standard test specimen in 50 ml. oftest lubricant at a temperature of 175C for 192 hours. High loadcarrying oils invariably cannot be made compatible with elastomers underthese conditions and so in a modification of this method a series oftests were carried out at different temperatures and a plot of percentelastomer swell versus temperature was made. The temperature(extrapolated) at which the zero swell occurs is given as an index ofelastomer compatibility of the oil. The results were as given in thefollowing table. It can be seen that the best results as regards E.P.properties are obtained when tetrabutyl ammonium salts of the di-methylhydrogen and methyl di hydrogen phosphates are used, and that the B1.properties fall rapidly as the chain length of the groups R and R in thephosphate in- When subjected to the IAE gear machine and Rolls RoyceSilicone Elastomer tests the following results were obtained.

IAE gear machine failure load 2000 rpm/110C Rolls Royce SiliconeElastomer Zero Swell 125C.

What is claimed is:

l. A lubricating oil composition comprising a lubricating oil to whichhas been added from 0.001 to 10 percent by weight, based on thelubricating oil, of a mixture of about equal molar proportions of (a) aquaternary hydrocarbyl ammonium salt of mono (C,C alkyl dihydrogenphosphate of the formula and (b) a quaternary hydrocarbyl ammonium saltof di- (C C alkyl hydrogen phosphate of the formula 11 0 \ONRIRIBHUwhere R, R R and R are similar or dissimilar hydrocarbon groups, R, R",R and R containing a total of at least 10 carbon atoms, and R and Rsimilar or dissimilar are C -C alkyl groups, said lubricating oilconsisting essentially of polyester of a polyhydric alcohol selectedfrom the class consisting of pentaerythritol, dipentaerythritol andmixtures of pentaerythritol and dipentaerythritol with a monocarboxylicacid or mixed monocarboxylic acids of from 4 to 10 carbon atoms.

2. A composition-according to claim 1 wherein the total number of carbonatoms in R, R R and R is at least 14.

creases. 3. A composition according to claim 2 wherein at TABLE CarbonChain Length Concentration IAE gear machine R-R Silicone Elastomer inacid phosphate wt.% P wt.% (amine salt) Failure Load 2000 Zero Swellmixture rpm/110C. 1b. Temp. (C)

l2 10 0.23 135 8 10" 0.20 132 6 10 0.19 125 4 10 0.17 63 2 10- 0.15 73 l7 X 10' 0.10 108 l 5 X 10 0.07 90 EXAMPLE 2 least two of the groups R, RR and R are the same.

Hexyl trioctyl ammonium salts of mixtures of methyl dihydrogen phosphateand dimethyl hydrogen phosphate were prepared by the same procedure ofExample 1 except that hexyl trioctyl ammonium hydroxide 4. A compositionaccording to claim 1 wherein R, R R and R are all n-butyl groups.

5. A composition according to claim 1 wherein R and R are both the same.

6. A composition according to claim 5 wherein R and R are both methylgroups or both ethyl groups.

7. A composition according to claim 1 which contains a mixture of hexyltrioctyl ammonium salts of methyl dihydrogen phosphate and dimethylhydrogen phosphate.

1. A LUBRICATING OIL COMPOSITION COMPRISING A LUBRICATING OIL TO WHICHHAS BEEN ADDED FROM 0.001 TO 10 PERCENT BY WEIGHT, BASED ON THELUBRICATING OIL, OF A MIXTURE OF ABOUT EQUAL MOLAR PROPORTIONS OF (A) AQUATERNARY HYDROCARBYL AMMONIUM SALT OF MONO (C1-C4) ALKYL DIHYDROGENPHOSPHATE OF THE FORMULA
 2. A composition according to claim 1 whereinthe total number of carbon atoms in R1, R2, R3 and R4 is at least
 14. 3.A composition according to claim 2 wherein at least two of the groupsR1, R2, R3 and R4 are the same.
 4. A composition according to claim 1wherein R1, R2, R3 and R4 are all n-butyl groups.
 5. A compositionaccording to claim 1 wherein R5 and R6 are both the same.
 6. Acomposition according to claim 5 wherein R5 and R6 are both methylgroups or both ethyl groups.
 7. A composition according to claim 1 whichcontains a mixture of hexyl trioctyl ammonium salts of methyl dihydrogenphosphate and dimethyl hydrogen phosphate.